In my work, we use gasses to cut steel. Usually, we use a combination of acetylene and oxygen, but we have used natural gas and propane as the fuel. The difference? BTU's. Acetylene burns hotter, so cutting steel is faster. Natural gas, or propane, doesn't release as much energy, so the process takes longer.
The same is true for automobiles and trucks. Gasoline, and diesel burn hotter, so you get more miles per gallon when used. Otherwise, the energy potential is much lower for natural gas and propane.
Years ago, some "brilliant" bureaucrat decided a certain number of miles driven by the TxDot employees should be in vehicles powered by natural gas or propane. It was a grand idea, except there weren't any such vehicles, which required the purchase, or retrofit of those in the fleet.
The retrofit vehicles could only be described as monsters of problems. The engines weren't designed for this fuel, so the problems of metering the fuel were a constant headache. Vehicles might just quit, or an incorrect fuel mixture could cause backfiring. The worst situation I saw was a truck backfired, the explosion blew the vacuum connection from the brake booster and the driver had to go to the shoulder when they couldn't stop in time to avoid an accident.
Even the new vehicles presented problems. Without a public fueling location, the drivers were forced to return to a central location; even if it meant driving over 80 miles to refuel. With the mandate of the type of fuel, switching to gasoline wasn't an option. The bureaucrats demanded the use, so they were forced to waste the fuel to satisfy the demand.
Overall, the costs must have been astronomical. Besides the extra costs per vehicle, the lack of BTU's meant that propane, or natural gas - which were almost as much per gallon - only allowed the vehicles to achieve about half the fuel mileage. If the truck got 18 mpg on gasoline, the "green" fuel only allowed around 9 to 10 mpg.
So, the entire endeavor was a terrible waste of tax dollars. The result? Who knows? There isn't any was to really determine the effect; especially with the distrust of scientist now that it's been proven many of the supposed scientific research wasn't scientific, or research for supposed AGW.
Politicians, and bureaucrats, have hurt this country worse than any foreign adversary. What makes this more terrible is the complacent nature of people to assume they're being well represented. Neither politicians, or bureaucrats give a rodent's fanny about your well being. They're in it for the power and your money.